1. Field of the Invention
The present invention relates to digital transmission techniques, and particularly to a cyclic prefix-based enhanced data detection method especially suited for the Orthogonal Frequency Division Multiplexing (OFDM) transmissions in the case of wired transmissions, or for Orthogonal Frequency Division Multiple Access (OFDMA) transmissions in the case of wireless transmissions.
2. Description of the Related Art
In a communication system, a transmitter sends data to a receiver through a channel. In the case of a wireless channel, the transmitted waveforms suffer from multipath fading due to reflection, refraction, and diffraction, which ultimately results in intersymbol interference (ISI) between the transmitted symbols. The motive of modern broadband wireless communication systems is to offer high data rate services. The main hindrance for such high data rate systems is multipath fading, as it results in ISI. It therefore becomes essential to use such modulation techniques that are robust to multipath fading.
Multicarrier techniques, especially Orthogonal Frequency Division Multiplexing (OFDM) (as used herein, the term Orthogonal Frequency Division Multiplexing is used to refer to frequency division multiplexing in both wired and wireless communications systems; hence it also encompasses Orthogonal Frequency Division Multiple Access) has emerged as a modulation scheme that can achieve high data rate by efficiently handling multipath effects. The additional advantages of simple implementation and high spectral efficiency due to orthogonality contribute towards the increasing interest in OFDM. This is reflected by the many standards that considered and adopted OFDM, including those for digital audio and video broadcasting (DAB and DVB), WIMAX (Worldwide Interoperability for Microwave Access), high speed modems over digital subscriber lines, and local area wireless broadband standards, such as the HIPERLAN/2 and IEEE 802.11a, with data rates of up to 54 Mbps. OFDM is also being considered for fourth-generation (4G) mobile wireless systems.
In order to achieve high data rate in OFDM, receivers must estimate the channel efficiently, and subsequently the data. The receiver also needs to be of low complexity and should not require too much overhead. The problem becomes especially challenging in the wireless environment when the channel is time-variant.
The techniques used for estimating the channel impulse response can be broadly divided into training-based, blind, and semi-blind techniques. In training-based technique, pilots, i.e., symbols that are known to the receiver, are sent with the data symbols. In the blind technique, the channel is estimated by using the structure of the communication problem, i.e., the natural constraints on data and channel, which include the finite alphabet constraint, the cyclic prefix, linear preceding, time and frequency correlation, and many more. Semi-blind techniques make use of both pilots and the natural constraints to efficiently estimate the channel.
Thus, an OFDM cyclic prefix-based enhanced data recovery method solving the aforementioned problems is desired.